We have developed a model system of phospholipid bilayer, azoinitiator and trialkylphenol to examine the effect of bilayer structure on free radical diffusion and on the efficiency of phenols as radical traps. We calibrated the azo initiator-phenol system against an azo initiator-I2 system in hydrocarbons and long-chain esters and found good agreement. In phosphatidyl choline bilayers (dipalmitoyl and dimyristoyl), the efficiency of the azoinitiator is lower than in bulk solvents by at least 20 percent. We propose to use this model system to evaluate the relative reactivity of different antioxidants, including tocopherol, in unreactive PC liposomes and later to examine the kinetic features of oxidation of reactive PC liposomes such as dilinoloyl phosphatidyl choline. Depending on the results of these experiments we will also evaluate the effect on free radical reactivity of changes in structure of the PC liposomes caused by incorporation of cholesterol and polypeptide.